Elements and Compounds Chapter 4B 

What is an Element? Definition: A pure substance that can not be broken down into simpler pure substances via chemical reactions. Examples: See element box The 94 Elements Project: Copper http://www.94elements.com/

What is a Compound? Definition: A pure substance which can be broken down into elements via chemical reactions. Examples: See compound box

Naming and Symbolizing Elements and Compounds Chemical Symbols for Elements – One or Two letter code Helpful to memorize 1st 20 plus Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Ag, I, Au, Hg Chemical Formulas for Compounds – Show how many of each type of atom is bonded together to form a molecule. Examples: H2O H2O2 CuO HNO3

Compounds vs. Mixtures Compound Mixture Properties of Compounds are different from those of components – Na + Cl = NaCl Definite Composition Cannot be separated by Physical Processes Properties of a mixture are a combination of the properties of the components - ethanol + water Variable Composition CAN be separated by physical means

Atoms and Molecules Atoms = smallest particle unique to an element. Molecule = group of atoms chemically connected or bonded together. Acquires distinct properties. Diatomic molecules = Two atoms of same type. Homoatomic molecule = one kind of atom Heteroatomic molecule = two or more different kinds of molecules. Molecules = Represented by chemical formulas

Try It! Write chemical formulas for molecules composed of One iron atom and one oxygen atom One carbon atom and four hydrogens One hydrogen, one carbon, and one nitrogen atom.

Natural Abundances Universe: 91% Hydrogen 9% Helium Earth’s Crust 60.1 % Oxygen 2.9% Hydrogen 20.1 % Silicon 2.6% Calcium 6.1 % Aluminum 2.4 % Magnesium 2.2 % Iron 2.1 % Sodium 1.5% All others

Natural Abundances Human Body 63 % Hydrogen 25.5 % Oxygen 9.5 % Carbon 1.4 % Nitrogen